Influence of Different Undercut Depths of Clasp Fabricated by Selective Laser Melting on Retentive Force.

INTRODUCTION: The purpose of this study was to investigate the influence of undercut depths on abutment teeth regarding the retentive force of clasps fabricated through selective laser melting (SLM), and to compare them with conventional cast clasps. METHODS: Akers clasps made of cobalt chromium alloy were fabricated using the SLM method (SLM), and the retentive forces were compared with clasps made with the conventional cast method (Cast). Three undercut amounts (0.25 mm, 0.15 mm, and 0 mm) were applied on the abutment tooth. The specimens were subjected to 10,000 repetitive insertion/removal cycles. RESULTS: SLM-0.15 showed slightly lower initial retentive force than the Cast specimens, it remained within an acceptable range. During insertion/removal test, the SLM-0.15 specimen showed a significant difference between the initial retentive force and the retentive force after 5,000 cycles, indicating that SLM-0.15 was the least likely to change in retentive force within the parameters established in this study. The inner clasp surface on the SLM groups had higher surface roughness before testing compared to the Cast specimen. CONCLUSIONS: Akers clasps fabricated by SLM demonstrated optimal initial retentive forces with smaller undercuts than conventional Cast clasps, and the retentive forces changed less with repetitive insertion/removal.

Influence of chewing force on salivary stress markers as indicator of mental stress.

The aim of this study was to investigate the influence of chewing force on salivary stress markers (alpha-amylase activity, salivary cortisol level and secretory immunoglobulin A secretion rate) as indicators of mental stress. Participants comprised 20 healthy men. The first set of saliva specimens (S1) was collected at immediately after a 20-min rest to evaluate stress markers. As stress loading, the participants were required to perform arithmetic calculations for 20 min, after which the second set of saliva specimens (S2) was collected. Each participant was then required to chew a piece of tasteless gum for 10 min, after which the third set of saliva specimens (S3) was collected. After a 20-min rest, the fourth set of saliva specimens (S4) was collected. Weak, habitual and strong chewing forces were assigned. Change rates of stress markers between S2 and S3, and S2 and S4 were calculated. A significant difference was observed in the change rate of cortisol levels between S2 and S3. Cortisol level decreased more under strong chewing than under weak chewing. No significant differences were observed in the change rate of amylase activity or s-IgA secretion rate among the three chewing forces. The results suggest that differences in chewing force influence the salivary cortisol level of the three stress markers, and that a strong chewing force induces a greater reduction in mental stress than a weak one.

Comparison of artificial tooth position in dentures fabricated by heat curing and additive manufacturing.

BACKGROUND: The purpose of this study was to compare the displacement of tooth arrangement in dentures fabricated by additive manufacturing (AM) and heat curing. METHODS: Three-dimensional (3D) scanning was performed for edentulous jaw models. After the teeth were arranged, 3D scanning for the wax denture was performed. Heat-cured dentures were fabricated with heat-cure polymer resin. Based on data obtained by subtracting the model data from wax denture data, AM dentures were fabricated from ultraviolet-cured acrylic resin. Accuracy was verified by superimposing heat-cured and AM dentures on the tooth region data from the wax dentures and measuring displacement of the tooth arrangement. RESULTS: In the maxillary dentures, the amount of tooth displacement for the heat-cured dentures and for the AM dentures ranged from -0.08 to +0.06 mm and from -0.25 to +0.06 mm respectively. A significant difference was observed between two dentures. In the mandibular dentures, the amount of tooth displacement for the heat-cured dentures and for the AM dentures ranged from -0.09 to +0.07 mm and from -0.03 to +0.07 mm respectively. No significant difference was observed between two dentures. CONCLUSIONS: The artificial teeth of the maxillary dentures fabricated by AM showed a greater displacement compared to those by heat curing.

Platelet activating factor antagonists: synthesis and structure-activity studies of novel PAF analogues modified in the phosphorylcholine moiety.

New analogues of platelet activating factor (PAF), in which the phosphate and trimethylammonium moieties were replaced with an acylcarbamoyl moiety and a quaternary cyclic ammonium group, were synthesized. Their biological activities as PAF antagonists were evaluated by the inhibition of PAF-induced rabbit platelet aggregation in vitro and protective effects on PAF-induced hypotension in rats and PAF-induced death in mice. Investigation of structure-activity relationships revealed that PAF antagonist activity is strongly influenced by the acyl substituent of the nitrogen atom on the carbamoyl group and the nature of the polar head group at the 3-position of the glycerin backbone. Among the compounds tested, 2-[[N-acetyl-N-[[2-methoxy-3-[ (octadecylcarbamoyl)oxy]propoxy]-carbonyl]amino] methyl]-1-ethylpyridinium chloride (21, CV-6209) was one of the most potent compounds in the in vitro assay (IC50 = 7.5 X 10(-8) M) and the most potent and long-lasting in the in vivo assays. (R)-(-)-21 and (S)-(+)-21 were also synthesized, and no significant differences were observed in PAF antagonist activity in vitro and an inhibitory effect on PAF induced hypotension in vivo between (RS)-21 and its enantiomers.

A simple CT method for location of auditory brain stem implant electrodes.

A method for locating auditory brain stem implant electrodes that have been placed in the lateral recess of the fourth ventricle is described. CT bone window images are "inverted" to black on white, then manually superimposed onto soft-tissue window images to enable identification of electrodes in relation to soft-tissue structures.

Toxicity testing of Senna occidentalis seed in rabbits.

The effect was investigated of administering ground Senna occidentalis seeds to rabbits in different concentrations (1%, 2%, 3% and 4%) in the ration. The experiment lasted 30 days and the toxic effects of the plant were evaluated on the basis of weight gain, histopathological, biochemical and morphometric parameters, as well as histochemistry and electron microscopy. Animals that received the ration containing 4% ground S. occidentalis seeds gained less weight (p < 0.05) and died in the third week. Histopathology revealed that the heart and liver were the main organs affected, with myocardial necrosis and centrolobular degeneration. There was a reduction in cytochrome oxidase activity in the glycogenolytic fibres, together with muscle atrophy, confirmed by the morphometric studies. Electron microscopy of the liver cells revealed dilated mitochondria, with destruction of the internal cristae.

Fatigue strength of Ce-TZP/Al2O3 nanocomposite with different surfaces.

Ce-TZP/Al(2)O(3) nanocomposite (NANOZR) has not only higher strength, but also higher fracture toughness than conventional Y-TZP, indicating its potential for use in dental implants. Surface treatment to obtain osseointegration, however, may alter its surface topography, thus affecting the cyclic fatigue strength that plays such an important role in the durability of this material. The aim of this study was to evaluate the influence of surface treatment on cyclic fatigue strength in NANOZR as compared with grit-blasted and acid-etched Y-TZP (125BE Y-TZP). Bi-axial flexure strength was measured in both static and cyclic fatigue tests, as recommended by ISO 6872. The cyclic fatigue test was performed by the staircase method in distilled water at 37°C, with a load of 10(6) cycles and 10 Hz. Bi-axial flexure strength of NANOZR was 1111-1237 MPa and 667-881 MPa in the static and cyclic fatigue tests, respectively. The bi-axial flexure strength of NANOZR under all conditions was greater than that of 125BE Y-TZP in the static and cyclic fatigue tests. The cyclic fatigue strength of NANOZR was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the promise of this material for use in dental implants.